Many electronic systems have a need to isolate electrical signals in one portion of the system from electrical signals in another portion of the system. In many control systems, for example, both high voltage and low voltage signals may be generated and monitored, and isolation between the signals is required for proper operation of the system. One reason such signals must be isolated is because the switching of high voltage signals can cause transients or noise on low voltage signals in the system. This noise on the low voltage signals, which would typically be digital logic level signals, can result in erroneous processing of the low voltage signals and thereby can result in improper operation of the overall system, as will be understood by those skilled in the art. Another reason for isolating signals may be safety, such as in medical systems where high higher voltages in portions of the system must be isolated from other portions that come into contact with a patient. In another situation, different grounds in different portions of a system need to be isolated from one another while allowing the communication of signals among the portions.
A variety of different devices and techniques have been utilized to communicate signals from one portion of a system to another portion of the system while maintaining isolation between the portions. Devices that provide this communication and isolation are generally referred to as data couplers. In operation, a data coupler receives an input electrical signal from a first portion of a system and converts this signal into a corresponding signal that is then communicated across an isolation barrier. The signal communicated across the isolation barrier is received and converted into an isolated output electrical signal that is then applied to a second portion of the system, with the received electrical signal corresponding to the input electrical signal from the first portion of the system.
Different types of data couplers use different types of isolation barriers to transfer or communicate signals from one portion of a system to another while maintaining electrical isolation between the portions. Each type of data coupler provides galvanic isolation between portions of the system, where galvanic isolation means the absence of any direct current (DC) path between the portions, as will be understood by those skilled in the art. Conventional data couplers utilize optical, magnetic, and capacitive isolation barriers to provide the required isolation and communication coupling path. For example, optical data couplers include an optical transmitter typically formed by a light emitting diode (LED) that receives an input electrical signal from a first portion of a system. The optical transmitter converts this signal into a corresponding optical signal that is communicated to an optical receiver, which is typically formed by a photodiode. In response to the received optical signal, the optical receiver generates a corresponding output electrical signal that is applied to a second portion of the system. In magnetic and capacitive data couplers, an input electrical signal is communicated through a transformer and capacitors, respectively, to provide a corresponding output signal, with the transformer and capacitors respectively providing the desired isolation between the input and output signals.
An acoustic data coupler includes piezoelectric elements coupled together through an acoustic coupling medium. The acoustic coupling medium acoustically couples the piezoelectric elements to one another and also provides the desired electrical isolation between the elements, with one element being coupled to a first portion of a system and the other element being coupled to a second portion of the system. In response to an input signal from the first portion, the first piezoelectric element generates an acoustic wave that propagates through the acoustic coupling medium to the second piezoelectric element. Responsive to the acoustic wave, the second piezoelectric element generates an output electrical signal that is applied to the second portion of the system.
The input signal applied to an acoustic data coupler is typically a digital signal having rising and falling edges that define bits of data being communicated by the signal. The precise manner in which transitions in the input signal are converted into a signal that is applied to the first piezoelectric element affects the overall operation, performance, and cost of the coupler. Moreover, while acoustic data couplers can potentially be utilized in a wide array of applications, improvements in existing couplers in terms of cost, data rates, and power consumption are needed. Another limitation with existing acoustic data couplers is channel density, meaning the size of existing couplers may be too large to allow the required numbers of couplers to be formed within a maximum specified space. Magnetically and capacitively isolated data couplers are further limited by susceptibility to external electromagnetic interference signals increasing the noise received in addition to the desired transmitted signal across the magnetic or capacitive isolation barrier. Acoustic data couplers rely upon acoustic waves between the piezoelectric elements rather than magnetic or capacitive coupling and have increased immunity allowing further improvements in performance and power consumption.
There is a need for circuits and methods for acoustic data couplers that improve the cost, data rate, power consumption, external electromagnetic noise immunity, and channel density or size of such couplers.